remove old flaky test

Author: ariebovenberg

tests/test_plain_datetime.py

@@ -1714,21 +1714,6 @@ def test_century_leap(self):
 
 
 class TestStartOf:
-    @pytest.mark.parametrize(
-        ("unit", "expected"),
-        [
-            ("year", PlainDateTime(2024, 1, 1)),
-            ("day", PlainDateTime(2024, 8, 15)),
-            ("hour", PlainDateTime(2024, 8, 15, 14)),
-        ],
-    )
-    def test_str_subclass(self, unit, expected):
-        class StrSubclass(str):
-            pass
-
-        dt = PlainDateTime(2024, 8, 15, 14, 30, 45, nanosecond=123)
-        assert dt.start_of(StrSubclass(unit)) == expected
-
     def test_year(self):
         dt = PlainDateTime(2024, 8, 15, 14, 30, 45, nanosecond=123)
         result = dt.start_of("year")